AB 1746-0W8 issue

The other day had a problem with a machine in which the output card indicator light was on but no 120v at the card. While checking the card I did see 120v for about 2 seconds and it was gone. I figured I had a faulty relay on the card so I switched the card out. Problem is still there--indicator light illuminated no 120v on the terminal. Changed out the rack---still have the problem. Switched to another output on another card. Never saw nothing like this. Any light on this problem would be appreciated. I'm very confused. Thanks to ALL-----Terry

You said you changed to another output on another card, what was the result?

Did th trouble follow the field device? If so, the circuit EXTERNAL to the card is probably drawing too much current for the output card to handle. Are you ABSOLUTELY sure the card is "relay out"?

Stationmaster

The problem child is O:2/2--switched to O:9/3. Started working. Before doing anything I applied 120v to the wire to verify wiring was good going the the solenoid. Ashort pulse to check it out.

Terry

Most interesting..... The only thing that springs to mind would be the output common supplied to that portion of the output card. Are both output cards the same type? #2 and #9?

As far as I know, nothing in the CPU, or program, or rack, should be able to turn on the output indicator led, and NOT turn on the output. That should be a function of the output card, it's common supply, and the load. (you did check for potential at the associated common supply to the card, right?)

If you figure it out, please post the solution....I'm quite curious.

Stationmaster

Just shooting from the hip here but, if you had something like this:

     Start      Stop                    O:2/2 

------| |-------|/|----------------------( )---

   |       |

   |       |

   | O:2/2 |

   ---| |---

 

 

That somehow got changed to this:

 

     Start      Stop                    O:2/2

------| |-------|/|----------------------( )---

   |       |

   |       |

   | O:2/2 |

   ---|/|---

And your scan time was low enough, couldn't that cause the LED to flash fast enough as to appear solid but not allow the relay to close before it is opened again? I've never tried it, but at 11:30PM, it looks right to me.

Also, I would do a cross reference (not find all) on O:2/2. Scroll up in the resulting window and look for anything that may be referencing the whole output word, like a MOV, MVM or COP statement.

If it comes back, I would suspect spikes and bad luck on the replacement card more than a programming error, but that is easy enough to rule out.

Have you had any rack faults? I have seen very weird behavior from a 1746-OW16 outputs 7 and 8 which are very near the backplane.

Spikes caused by inductive load were causing backplane noise, misinterpreted by the scanner (remote rack) as the adjacent or undetermined slot faults.

It also resulted in a couple of occurences of the LED not matching the relay state, but this was shortly followed by rack faults. I was able to detect retries and errors on the scanner diagnostic integers only when output points 7 and 8 were fired.

Changing to a triac card and adding surge suppression was the fix in my case. I have seen this twice on isolated systems.

Probably you just got a bad spare card, but it might be useful to measure the peak current draw of the solenoid, verify the surge suppresion, and/or fuse it...but I would not worry about it unless it comes back...

Paul

Had no faults at all. It's just O:2/2 indicator light was illuminated and no out at the card?? When the line goes downI will dig a little deeper. Thanks to all...

Are the rest of the outputs from card 2 working ok.

I tend to agree with Magicsmoke. Have had the problem once before on the connector block, not AB, but did send me in a spin for a while


Brian